A. V. Konovalov

Modelling and Simulation of Strain Resistance of Alloys Taking into Account Barrier Effects

The paper proposes a model of strain resistance of alloy under high-temperature deformation. The model describes hardening of alloy due to the increase of dislocation density, as well as the barrier effect of blocking free dislocations, boundaries of grains and subgrains by dispersoids. The model also takes into account the softening processes associated with the recovery and dynamic recrystallization. The model has been tested on the rheological behavior of an Al-Mg alloy named AMg6 at temperatures of 400 and 500 oC in the range of strain rates from 5 to 25 s. It was found in this temperature – strain rate range that the curve of strain resistance of the AMg6 alloy consists of several portions. First there is hardening of the material, then there is material softening, which is again replaced by hardening of the material. With the use of the electron backscatter diffraction technique and transmission electron microscopy, it was found that the main process of softening at investigated temperatures is dynamic recrystallization. The appearance of the second portion of hardening on the strain resistance curve is the inhibition of dynamic recrystallization, as well as manifestation of the barrier effect of blocking free dislocations, grain and subgrain boundaries by dispersoids.

A hierarchial modeling of stress-strain state of multiphase material subjected to uniaxial loading

On the example of an Al/SiC metal matrix composite, we propose a numerical study of multiphase material stress-strain response evolution using the structural-phenomenological approach. The study covers micro- and macrolevel analyses of uniaxial tension and compression and takes material rheology and internal structure into consideration. We describe features of the emergence of stress concentration regions leading to local plastic deformation causing a heterogeneous stress-strain state on the microlevel. We depict a strain dependence of the stress stiffness coefficient and the Lode-Nadai coefficient fields.

Determination of metal strain-hardening curves from conical-indenter impression results

A new technique to determine the strain resistance of metal with a pronounced yield strength is proposed. As an approximation of the curves of the strain-hardening resistance of metals, a three-parameter function is used, which optimally describes the form of real curves. Three conical indenters with different taper angles are used. Multiple simulations of indenter impression into a metal by the finite-element method are carried out. As a result, a functional correlation is found between the parameters of the function approximating the hardening curves and the diagrams of conical-indenter impression into an elastoplastic medium. It is experimentally shown that the curves of strain hardening can be quite accurately determined by the proposed technique.

An approach to the parallel assembly of the stiffness matrix in elastoplastic problems

When modeling deformation process by the finite element method (FEM), it is necessary to solve a system of simultaneous linear algebraic equations (SLAE) with a large sparse matrix. In addition to the high computational complexity of the linear system solution process, obtaining a system matrix from a finite element model also demands significant computational resources. This process is termed a stiffness matrix assembly. The paper suggests an approach to the stiffness matrix assembly. According to this approach, matrix components are calculated individually and independently and their arrangement is made through a special data structure managing computer memory and providing thread synchronization. The data structure consists of an unrolled list array and allows us to assemble the stiffness matrix for a time proportional to the number of mesh nodes for any practically used finite element mesh. The approach is effective for complex models with heterogeneous finite elements, in particular, in elastoplastic...

Peculiarities of the rheological behavior and structure formation of aluminum under deformation at near-solidus temperatures

This paper deals with a peculiar rheological behavior of aluminum at near-solidus temperatures. It has been experimentally established that there is an inverse strain rate dependence of strain resistance at temperatures ranging between 560 and 640°С and strain rates ranging from 0.06 to 1.2 s−1. Electron backscatter diffraction analysis has shown that at temperatures ranging between 540 and 640°С and strain rates ranging from 0.06 to 0.1 s−1, the main process of softening is dynamic polygonization, resulting in in situ recrystallization. At higher strain rates, ranging between 0.8 and 1.2 s−1, and temperatures ranging between 560 and 640°С, the recovery is dynamic. This unusual behavior of the mechanism of softening and the presence of the inverse strain rate dependence of strain resistance can be explained by blocking the motion of free dislocations by foreign atoms, which occurs at strain rates ranging between 0.06 and 0.1 s−1. This process results in dislocation pile-up, thereby causing in situ recrystallization. At strain rates exceeding 0.16 s−1, there is no intensive blocking of dislocations, leading to a direct strain rate dependence of strain resistance.

Effect of silicon carbide particles on the mechanical and plastic properties of the AlMg6/10% SiC metal matrix composite:

This work deals with studying the effect of reinforcing SiC particles on the mechanical and plastic properties of a metal matrix composite with a matrix of aluminum alloy AlMg6 (the 1560 aluminum alloy according to the Russian State Standard GOST 4784−97). We assess this effect using the results of mechanical tests at the microscale and macroscale levels. The paper analyzes the fracture mechanism at the microlevel under tensile and compressive stress conditions, as well as the type of contact between the composite constituents. The experimental results obtained for the metal matrix composite are compared with analogous experimental data for the AlMg6 alloy and a compacted material made from the AlMg6 alloy (a compacted powder without addition of SiC reinforcing particles). The studied compacted materials were not previously subjected to extrusion. The tests show a decisive influence of the reinforcing particles on the plastic and mechanical properties of the AlMg6/10% SiC metal matrix composite under compression and tension. For example, the addition of silicon carbide increased the initial yield stress of the compacted material by 26% under tensile tests, and the percentage elongation after fracture was increased up to 1.1%, while it amounted to 0.02% for the compacted material without addition of silicon carbide. Under compression, on the contrary, the addition of silicon carbide degraded plastic properties. As a result, the percentage compression before cracking was 28.4% and 57.9% for the compacted materials with and without addition of silicon carbide, respectively.

A gravitational approach to modeling the representative volume geometry of particle-reinforced metal matrix composites

Computational models of representative volumes of metal matrix composites are crucial for investigating material behavior on the microscale. Numerical simulations often employ finite element models of representative volumes. Such models are based on observations of material microstructural properties, for example, by means of electron microscopy. Constructing a geometrical model of a representative volume for further computations can be a tedious task. This paper presents a new approach to creating geometrical models of this kind. The approach is based on the simulation of rigid body motion in a gravitational field and allows one to automatically generate geometrical models of representative volumes. The approach capabilities are exemplified by two geometrical models of representative volume. One model describes a metal matrix composite with high volume fraction of prismatic reinforcement particles, produced by liquid metal infiltration. The other model describes a metal matrix composite with high volume fraction of metal pellets, produced by powder metallurgy.

COMPUTER-AIDED INTERSUBJECTIVE ASSIGNMENT OF OVERLAPS FOR SHAFT-TYPE FORGINGS

The paper exemplifies the mechanism of choosing an intersubjective (rational) decision from a set of acceptable decisions by computer-aided assignment of overlaps for shaft-type forgings. Goals are formulated and formalized; membership functions of possible decisions corresponding to the set goals are defined. A criterion for the selection of a rational variant of overlap assignment from a set of acceptable decisions is developed.

Intersubjective decision-making for computer-aided forging technology design

We propose a concept of intersubjective decision-making for problems of open-die forging technology design. The intersubjective decisions are chosen from a set of feasible decisions using the fundamentals of the decision-making theory in fuzzy environment according to the Bellman-Zadeh scheme. We consider the formalization of subjective goals and the choice of membership functions for the decisions depending on subjective goals. We study the arrangement of these functions into an intersubjective membership function. The function is constructed for a resulting decision, which is chosen from a set of feasible decisions. The choice of the final intersubjective decision is discussed. All the issues are exemplified by a specific technological problem. The considered concept of solving technological problems under conditions of fuzzy goals allows one to choose the most efficient decisions from a set of feasible ones. These decisions correspond to the stated goals. The concept allows one to reduce human participation in automated design. This concept can be used to develop algorithms and design programs for forging numerous types of forged parts.We propose a concept of intersubjective decision-making for problems of open-die forging technology design. The intersubjective decisions are chosen from a set of feasible decisions using the fundamentals of the decision-making theory in fuzzy environment according to the Bellman-Zadeh scheme. We consider the formalization of subjective goals and the choice of membership functions for the decisions depending on subjective goals. We study the arrangement of these functions into an intersubjective membership function. The function is constructed for a resulting decision, which is chosen from a set of feasible decisions. The choice of the final intersubjective decision is discussed. All the issues are exemplified by a specific technological problem. The considered concept of solving technological problems under conditions of fuzzy goals allows one to choose the most efficient decisions from a set of feasible ones. These decisions correspond to the stated goals. The concept allows one to reduce human particip...

Modeling the stress-strain state of the V95/SiC aluminum alloy matrix composite under uniaxial loading

In the paper we develop a computational model of plastic deformation of an aluminum matrix composite. The composite is produced by sintering, and it has a cellular microstructure. SiC reinforcement particles form a stratum along the pellet boundaries of the V95 (analogous to 7075) aluminum alloy. The effective properties of the plastic flow of the stratum material are obtained by the rule of mixtures, depending on the volume fractions of the aluminum alloy and the reinforcement particles in the composite material. The feasibility of the model is demonstrated on the example of numerical simulation of the micro- and macroscopic stress-strain state of the composite under uniaxial tensile and compressive loading conditions.